Production of shaded glazes



Patented Feb. 3, 1953 FRODUCTION OF SHADED GLAZES Leon J. Le Clercq, Glendale, Calif., assignor to Gladding, McBean & 00., Los Angeles, Calif., a corporation of California No Drawing. Application May 2, 1949, Serial No. 91,017

4 Claims.

This invention relates to the production of shaded glazes and is particularly directed to a method of producing ceramic objects provided with a single continuous glaze over their surface, desired areas of said glaze differing in color from other areas so as to form a desired decorative design.

I-Ieretofore ceramic objects have been provided with either transparent or opaque glazes and in known manners various colors can be imparted to the glaze. Each glaze composition, however, is capable of producing but a single color at maturity under standard firing conditions. In the event it was desired to produce a varicolored design upon the surface of the ceramic object, different glazes were applied to different areas of the surface, or a single glaze was first applied over the entire surface and then desired areas of the surface were covered with a second and differently colored glaze.

Objects such as ceramic tile, chinaware, dishes, vases, etc., which were to be decorated with a plurality of colors or shades required the separate application of a plurality of different glaze compositions. The superimposition of glazes, one over the other, was not only difiicult, but in many instances, produced an uneven surface to the object, greater glaze thickness existing in one area than in another. By reason of variation in the thickness of the glaze in different portions of the object, stresses were often set up in the glaze causing the development of checks or crazing.

The present invention is based upon the discovery that a single glaze composition normally capable of maturing to be a single uniform color can be caused to mature into various shades or colors without the application of over-glazes or different glaze compositions and without deviation from the standard or customary firing conditions.

The present invention, therefore, permits the production of especially beautiful ceramic objects with a surface glaze of uniform thickness, desired area of such glaze exhibiting deviations from the normal color of the glaze composition, thereby imparting shadings, designs and decorative features to the. ware of a character not attained heretofore.

Furthermore, the method of the present invention is applicable to either a single fire process or the normal two-fire process. lhe glaze composition employed may be applied directly to the unfired ware or object, or to the bisque.

Generally stated, it has been discovered that changes in the maturing color of a glaze composition can be obtained in localized and desired areas by applying to such areas of the surface of the object, after the application of a glaze composition and before firing, very finely divided silicon carbide. The glaze composition employed should contain coloring ingredients in the form of metallic oxides capable of being reduced, such metallic oxides being of a different shade or color upon reduction than the color or shade normally developed by said oxides in the customary or usual firing atmosphere.

It is an object of the present invention, therefore, to disclose and provide a simple and efficient method of producing ceramic objects provided with a single continuous glaze, desired portions of such glaze differing in shade or color from other portions thereof, whereby decorative effects are readily btained.

A further object of the invention is to disclose and provide a novel method of controlling the shade or color of a surface glaze on a ceramic body in localized and desired areas thereof.

Again, an object of the invention is to disclose methods of employing silicon carbide as a means for varying the shade or color of a ceramic glaze composition within localized areas.

A still further object of the invention is to disclose and provide novel and attractive ceramic objects provided with a single continuous glaze of virtually constant thickness, such glaze exhibiting desired changes in shade or color in specified and limited areas.

These and other objects and advantages of the invention will become apparent to those skilled in the art from the following description of ex emplary modes of operation.

Colored glaze compositions, Whether raw glazes or fritted glazes, may be employed in carrying out the process embodied herein, but in all instances the glaze composition must contain metallic oxides or pigments capable of chemical reduction with accompanying change in shade or color. Since the manufacture of glaze compositions is well known in the art and the fitting of a glaze to a body is also well known, these details need not be repeated here.

Suffice it to say that a suitable glaze composition containing the desired oxides, and in a suitable state of fine division, is applied to the ceramic object; said object being either in the dried or leathery state or in the bisque state. In some instances the object may be provided with an engobe, although the use of an engobe is ordinarily not necessary unless the surface glaze is of a transparent nature upon maturity.

The glaze composition may be applied to the ceramic object either as a suspension or slip,

and it may be applied by painting, spraying, dipping or brushing, although spraying and dipping are the most economical and widely applied modes of application.

After the glaze composition has been applied to the object and before such object is subjected to firing in a kiln of suitable type (mufiies, continuous kilns or downdraft kilns may be used) desired areas of the surface coated with the glaze composition are now treated with very finely divided silicon carbide. The silicon carbide is preferably in such fine state of division that it will virtually completely pass through a 280 or 320-mesh sieve. The so-called airfloated silicon carbide powders may be used; such powders being composed of particles which would pass a theoretical 600 to IOU-mesh sieve. This very finely divided silicon carbide may be applied to the surface carrying the unmatured, relatively freshly applied glaze composition in a number of different ways.

If the glaze composition applied to the surface of the object has been dried, the silicon carbide may be applied to desired areas of such surface in the form of a spray through a stencil. The silicon carbide may be dispersed in an aqueous medium containing a small amount of organic, non-ash forming gum, resin, starch, or the like, to permit adherence of the fine silicon carbide particles to the surface of the unmatured glaze composition.

The silicon carbide suspension or dispersion may also be applied to desired areas of the unmatured glaze composition by means of a brush.

The silicon carbide particles may also be applied to the surface of the unmatured glaze composition by means of a decalcomania. The latter method has advantages in that more accurate control may be attained both as to quantity of silicon carbide applied per square inch of surface and the contours of the design or area which is being covered with the silicon carbide.

Moreover, it may be highly desirable to cover a selected area of the surface of the unfired glaze composition with a very dilute suspension of silicon carbide and then within the area thus covered, secondary applications of silicon carbide can be made by means of a brush so as to increase the quantity of silicon carbide only within secondary, smaller areas. For example, an area having a contour of a leaf may be sprayed with a relatively dilute dispersion of silicon carbide and then the veins of such leaf may be painted with a more concentrated suspension of silicon carbide so as to eventually accentuate differences in shading in the portions representing the veins of the leaf.

After the object has been treated in the manner described hereinab'ove it is subjected to firing under the normal atmospheric condition customarily employed in maturing the glaze composition or the glaze composition and body. In other words, in the event oxidizing conditions are normally used, such oxidizing atmospheric conditions are employed during the burning of objects prepared in the manner stated. As previously indicated, this burning may be termed a glost burn (if the glaze composition has been applied to a bisque) or the burning or firing may simultaneously mature both the body and the glaze. Time and temperature of burning customarily used in maturing the body or glaze composition are employed in the burning of objects treated as hereindescribed.

When the objects are removed from the kiln it will be found that the areas to which the silicon carbide has been applied exhibit a color differing materially from the color exhibited by the glaze composition in other areas of the object. If, for example, the glaze composition contained chromium, antimony and tin, and the glaze composition has matured to produce a coral shade, it will be found that the limited areas to which silicon carbide has been applied are now yellow. As a result, the finished object is provided with a single continuous glaze of uniform thickness, but the selected areas are yellow Whereas the background or other areas are coral.

In the event the glaze composition contained manganese and cobalt in proper proportions (as is known in the art) such glaze would have matured to a gray color, but those limited areas to which silicon carbide had been applied are now blue. In the event the glaze composition originally applied contained chrome and tin it will be found to have matured to a desired shade of pink or maroon, but the design to which silicon carbide had been app-lied is now clear or white.

It is to be understood that, as indicated hereinabove, the extent to which departures from the original color of the glaze are attained depends somewhat upon the concentration of silicon carbide applied to the desired area. If an extremely dilute suspension of silicon carbide had been originally used, only a minor bleaching of the original or primary color of the glaze composition is attained. It is for this reason that two or even three shades or tones may be obtained within a given area from the same basic glaze composition, these shades or tones depending upon the amount of silicon carbide per square inch of surface which has been applied thereto. In all instances, however, the quantities applied are very small, equivalent to those deposited by the use of a rather thin liquid suspension upon the surface of a bisque body by means of a brush.

It will be noted, therefore, that the present process does not impair normal firing schedules or firing conditions; it does not require the finished product to be subjected to additional handling or treatment after firing. The effects obtained are strikingly different from those heretofore obtained in the ceramic arts. Moreover, the glazed surface obtained on the objects is uniformly free from crazing or other undesirable characteristics and the silicon carbide treatment does not in any way impair the original characteristics of the overglaze initially applied to the objects.

All changes and modifications coming within the scope of the appended claims are embraced thereby.

I claim:

1. A method of producing ceramic objects provided with a single continuous overglaze having areas differing in color from other areas, which comprises: applying a glaze composition containing reducible oxide coloring components to the surface of a ceramic object; applying a dis-continuously associated layer of silicon carbide in a state of fine division to desired areas only of the surface covered by said glaze composition; and firing the object in an oxidizing atmosphere to mature the glaze.

2. A method of the character stated in claim 1 wherein the silicon carbide is sprayed upon the desired areas of the surface covered by the glaze composition.

3. A method of the character stated in claim 1 wherein the silicon carbide is applied to an unfired ceramic object and both the object and the glaze compositions are matured during a single burning operation, the glaze composition exhibiting a difierent color in the area to which silicon carbide had been applied than in other areas.

4. A method of the character stated in claim 1 wherein the layer of silicon carbide is formed by applying a dispersion of finely divided silicon carbide in an organic gummy medium.

LEON J. LE CLERCQ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date Rowland Dec. 9, 1930 Hunt et al. Jan. 15, 1935 Schramm Sept. 26, 1939 Scheetz Feb. 23, 1943 FOREIGN PATENTS Country Date Great Britain 1903 Great Britain Feb. 13, 1913 Great Britain Oct. 2, 1930 

1. A METHOD OF PRODUCING CERAMIC OBJECTS PROVIDED WITH A SINGLE CONTINUOUS OVERGLAZE HAVING AREAS DIFFERING IN COLOR FROM OTHER AREAS, WHICH COMPRISES: APPLYING A GLAZE COMPOSITION CONTAINING REDUCIBLE OXIDE COLORING COMPONENTS TO THE SURFACE OF A CERAMIC OBJECT; APPLYING A DISCONTINUOUSLY ASSOCIATED LAYER OF SILICON CARBIDE IN A STATE OF FINE DIVISION TO DESIRED AREAS ONLY OF THE SURFACE COVERED BY SAID GLAZE COMPOSITION; AND FIRING THE OBJECT IN AN OXIDIZING ATMOSPHERE TO MATURE THE GLAZE. 